Feign源码分析之FeignClientFactoryBean

springcloud-openfeign-core-2.1.1.release.

继上篇Feign源码分析之EnableFeignClients后，Springcloud中将FeignClient注解的接口封装到FeignClientFactoryBean中，现在来看看FeignClientFactoryBean的实现。

Feign源码分析之FeignClientFactoryBean-LMLPHP

图1

其属性如List-1所示，这些属性的值都是在FeignClientsRegistrar中设置的。

List-1

class FeignClientFactoryBean
		implements FactoryBean<Object>, InitializingBean, ApplicationContextAware {

	/***********************************
	 * WARNING! Nothing in this class should be @Autowired. It causes NPEs because of some
	 * lifecycle race condition.
	 ***********************************/

	private Class<?> type;

	private String name;

	private String url;

	private String contextId;

	private String path;

	private boolean decode404;

	private ApplicationContext applicationContext;

	private Class<?> fallback = void.class;

	private Class<?> fallbackFactory = void.class;
...

由于实现了FactoryBean接口，我们来看最重要的getObject()方法，如List-2，getTarget方法中首先从Spring上下文中获取FeignContext。FeignContext是在FeignAutoConfiguration中注册到Spring容器中的，如List-3所示，会将spring容器所有的FeignClientSpecification放入到FeignContext中，FeignClientSpecification在Feign源码分析之EnableFeignClients中讲过，即EnableFeignClients的defaultConfiguration。

List-2

@Override
public Object getObject() throws Exception {
    return getTarget();
}

<T> T getTarget() {
    FeignContext context = this.applicationContext.getBean(FeignContext.class);
    Feign.Builder builder = feign(context);
...

List-3

public class FeignAutoConfiguration {
	@Autowired(required = false)
	private List<FeignClientSpecification> configurations = new ArrayList<>();

	@Bean
	public HasFeatures feignFeature() {
		return HasFeatures.namedFeature("Feign", Feign.class);
	}

	@Bean
	public FeignContext feignContext() {
		FeignContext context = new FeignContext();
		context.setConfigurations(this.configurations);
		return context;
	}
...

List-2中，得到FeignContext后，调用feign方法，从FeignContext中获取Encoder、Decoder、Contract，其实内部是从spring容器中获取的，得到Feign.Builder。

我们可以实现RequestInterceptor接口，之后交给Spring容器，feign会自动加上这个拦截器，这个的实现也在FeignClientFactoryBean中，在configureUsingConfiguration方法中，如下List-4

List-4

Map<String, RequestInterceptor> requestInterceptors = context
.getInstances(this.contextId, RequestInterceptor.class);
if (requestInterceptors != null) {
    builder.requestInterceptors(requestInterceptors.values());
}

List-4中的context.getInstances()方法内部是如何实现的呢。来看下FeignContext的父类NamedContextFactory，List-5中的setConfigurations方法在List-3中调用，在构造FeignContext的时候调用的。

List-5

public void setConfigurations(List<C> configurations) {
    for (C client : configurations) {
        this.configurations.put(client.getName(), client);
    }
}

List-6中

getConext方法获取ApplicationContext，之后从该ApplicationContext中获取bean
getConext方法中，如过name对应的ApplicationContext不存在，则调用createContext方法进行创建
AnnotationConfigApplicationContext.register方法把配置类注册到ApplicationContext中，还设置了AnnotationConfigApplicationContext的parent为当前Spring上下文，这样当在AnnotationConfigApplicationContext中获取不到bean时，就会从父ApplicationContext中获取

List-6

public <T> T getInstance(String name, Class<T> type) {
    AnnotationConfigApplicationContext context = getContext(name);
    if (BeanFactoryUtils.beanNamesForTypeIncludingAncestors(context,
            type).length > 0) {
        return context.getBean(type);
    }
    return null;
}

protected AnnotationConfigApplicationContext getContext(String name) {
    if (!this.contexts.containsKey(name)) {
        synchronized (this.contexts) {
            if (!this.contexts.containsKey(name)) {
                this.contexts.put(name, createContext(name));
            }
        }
    }
    return this.contexts.get(name);
}

protected AnnotationConfigApplicationContext createContext(String name) {
    AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
    if (this.configurations.containsKey(name)) {
        for (Class<?> configuration : this.configurations.get(name)
                .getConfiguration()) {
            context.register(configuration);
        }
    }
    for (Map.Entry<String, C> entry : this.configurations.entrySet()) {
        if (entry.getKey().startsWith("default.")) {
            for (Class<?> configuration : entry.getValue().getConfiguration()) {
                context.register(configuration);
            }
        }
    }
    context.register(PropertyPlaceholderAutoConfiguration.class,
            this.defaultConfigType);
    context.getEnvironment().getPropertySources().addFirst(new MapPropertySource(
            this.propertySourceName,
            Collections.<String, Object>singletonMap(this.propertyName, name)));
    if (this.parent != null) {
        // Uses Environment from parent as well as beans
        context.setParent(this.parent);
        // jdk11 issue
        // https://github.com/spring-cloud/spring-cloud-netflix/issues/3101
        context.setClassLoader(this.parent.getClassLoader());
    }
    context.setDisplayName(generateDisplayName(name));
    context.refresh();
    return context;
}

Reference

源码，github地址略

克虏伯

Feign源码分析之FeignClientFactoryBean

Reference